Relay



Dec. 26, 1944- A. L. w. WILLIAMS RELAY Filed April 9, 1942 INVENTOR. AmmLw. Vuums Patented Dec. 26, 1944 RELAY Alfred L. w. Williams, Cleveland Heights, Ohio, assignor to The Brush Development Company,

Cleveland, Ohio, a corporation of Ohio Application April 9, 1942, Serial No. 438,288

iCl. 175-9320) 22 Claims.

This invention relates to electrically operated relays and mor particularly to piezoelectric apparatus and circuits.

Numerous attempts have been made to successfully utilize Rochelle salt piezoelectric crystal elements of the Bimorph type or of the single plate bender type, in relays and the like, as exemplified by the relay system disclosed in the Hearn Patent 2,182,340. Theoretically, the piezoelectric crystal element is an ideal substitute for an electromagnetic relay because of the fact that it responds substantially instantaneously te minute increments of energy. Workers in the art prior to this invention, however, appear to have been unable to counteract a very troublesome characteristic of certain piezoelectric crystal elements namely, their tendency to set or sag from natural causes after having been in use for a more or less extended period. Such sagging or setting results in a change in the contact-spacing with the result that very often piezoelectric crystal element relays become inoperative long before they wear out.

The problem of uccessfully utilizing a piezoelectric element in a relay is also aggravated by the extremely small amplitude of movement of the element, which is of the order of magnitude of only two to four ten-thousandths of an inch. Contact point spacing, even under most favorable conditions, is difficult to obtain and maintain by usual methods and one of the primary objects of my invention, therefore, is to provide a piezoelectric relay that shall not require critical spacing of the contact points.

Another object of this invention is to provide a relay of the piezoelectric type that shall be immune to the deleterious efiect of set.

Another object of this invention is to provide a relay wherein minute movements of a piezoelectric element are integrated to give rise to a greater movement of a circuit opening and/or closing device.

Another object of this invention is to provide a relay that shall be positive in its response to even the most minute movements of a piezoeletric element.

Another object of this invention is to provide a piezoelectric relay, of the polarized type,-which is independent of contact spacing and crystal element set.

Anotherobject of this invention is to provide a piezoelectric relay wherein time delay, either in closing or in opening the secondary circuit, may be predetermined with accuracy without resorting to electrical means.

Another object of this invention is to provide a piezoelectric conversion device analogous to a relay whereby alternating primary control potentials may be converted into controlled alternating potentials at a predetermined lower frequency.

Another object of this invention is to provide a piezoelectric conversions device analogous to a relay whereby unidirectional control potentials may be converted into controlled alternating potentials at a predetermined frequency.

A still further object of this invention is to provide a piezoelectric relay that shall be substantially immune to climatic efiects.

In a preferred embodiment of this invention, the foregoing objects and other objects ancillary thereto are attained by providing a relay of the closed circuit type i. e., one wherein the secondary contacts are normally biased into engagement and are opened only during actuation of the relay from the control circuit.v Further more, instead of utilizing one or more fixed contact points that engage the contact or contacts carried on or actuated by the crystal element, there may be substituted therefor, according to this invention, an oscillatory device and provide means for biasing or urging it against a crystal-element-actuated contact point. Accordingly, set or sag of the crystal element is compensated and the most pronounced inherent disadvantage of crystal elements when utilized for relay-actuation is overcome.

Another important feature of this invention resides in the provision of means whereby the time lag between application of the controlling potential and the closing of the secondary contact points may be accurately predetermined. For

' that purpose, use of a metallic body or other dc.-

vice having predetermined inertia, such as a pendulum, a spring-supported weight, or the like, may be made, the time delay being fixed by the mass and the restoring force applied thereto. Alternatively, the mass may take the form of an element analogous to a see-saw, the moment of one end about the point of support being slightly greater than the moment of the other part, the heavier part normally engaging the movable contact point actuated by the piezoelectric crystal element. Further, if desirable, biasing means such as a small spring or the like in addition to gravity may be utilized.

In the embodiment of this invention last described, the rotary movement of the pivoted device, after having been given an initial impulse by the contact point carried by the crystal element,'may be limited by a resilient stop which may form the fixed contact point of a secondary or controlled circuit.

When it is desired to utilize the improved relay as a self-excited buzzer or conversion device, both the contact point carried by the crystal element and also the oscillatory device itself, or a contact point moved thereby, may be interposed in the primary or control circuit.

7 The novel features of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation together with further objects and advantages thereof, will best be understood from a consideration of the following description of certain specific embodiments taken in connection with the accompanying drawing in which:

Figure 1 is a diagrammatic view exemplifying an embodiment of this invention;

Figure 2 is a diagrammatic view exemplifying an alternative embodiment of this invention;

Figure 3 is a diagrammatic view exemplifying the application of this invention to conversion devices of the so-called "buzzer" type, and

Figure 4 is a diagrammatic view of a still further embodiment of this invention. In all figures of the drawing identical elements are similarly designated.

Referring now to Figure l of the drawing, a preferred embodiment of this invention comprises a piezoelectric element, designated generally by the numeral I, fixed at one end, 3, the free end 5 thereof being adapted to bend or flex when electrical potential of the proper polarities are applied to the element. Purely for exemplification purposes a piezoelectric element of the bender Bimorph type constituted by two plates 1, i cut from a Rochelle salt crystal with their principal faces parallel to the Y and Z axes and perpendicular to the Xaxis of the original crystal vided with an outer electrode i, the two outer electrodes being electrically interconnected. Because of the restraining action of each crystal section upon the other, when electrical potentials are applied between th inner and outer electrodes one section tends to expand longitudinally while the other tends to contract. As a result or" the restraining action of each element upon the other element cemented thereto, the simultaneous elongation and contraction is transformed into a bending moment around the fixed end 3 of the Bimorph."

The free end 5 of the crystal assembly carries a contact point 13 which may be metallic or which may be made of any suitable non-conductive material such as rubber, Bakelite," Viscoloid, etc., if the said contact point is not to be utilized as part of the electric circuit hereinafter to be explained more in detail.

Associated with the crystal-carried contact point but not mechanically connected to the crystal element is an independent oscillatable device which, for purposes of explanation, is illustrated as a substantially balanced electrically conductive see-saw l5, pivotally mounted in its center and iii) IS in the direction of the arrow A. The bias may be obtained by making that portion of the device adjacent to the Bimorph slightly heavier than the other portion. If desired, a small bias-spring may be utilized as well. The normal position, therefore, of a contact point I! carried by the pivoted device 15 is in engagement with the crystal-carried contact point l3 and no matter how much the latter may vary in position because of sag or set of the crystal element, the operation of the relay is not interfered with.

As shown by the dotted lines in Figure 1, the pivoted oscillatable device l5 may move in the direction of the arrow B to engage a resilient contact element I! that is included in a secondary controlled circuit. Such circuit may comprise a potential supply 2|, a controlled device 23, and an electrical connection 25 to a second contact point 21 carried by the oscillatable device. The connection may be by way of a slip ring 28 carried by the device l5. Alternatively, the main body of the oscillatable device l5 may be removed entirely from the electrical circuit and a switch point 3 l, as indicated in dotted lines, may be utilized in connection with the resilient contact element IS. A capacitor 32 may be connected across the contacts of the secondary circuit as is customary in analogous devices for the prevention of injurious sparking,

To explain the operation of this novel relay, let us first assume that the contact point carried by the oscillatable device is resting upon the crystal-carried contact point. If, now, the primary or controlling circuit is momentarily closed by a switch 33 or the like, and either'a suiliciently high unidirectional potential of the proper polarity from a suitable source 35, or an alternating potential be applied across the crystal electrodes 9 and H,.the device [5 will be given a sharp impulse in the direction of the arrow B and, because of its inertia, it will leave the crystal-carried contact point l3 and rotate until it engages the fixed resilient contact element I 9 to close the secondary or controlled circuit. The dwell" of the oscillatory device against the resilient element I9 is determined by the inertia of the device, by the compliance of the said element and the restoring force exerted by gravity. Any reasonable duration of engagement may be obtained. The oscillatable device I5 returns toward its normal or rest position a predetermined interval after the secondary circuit is initially closed. If the primary or controlling potential is only momentarily applied, nothing further happens until the switch 33 is once more closed. In the event that the primary controlling circuit supplies alternating potential to the crystal electrodes, and the switch is kept closed, the crystal element continues to vibrate; but the secondary circuit, because of the dela action described, is made and broken periodically. It will thus be obvious that, if the period is low in comparison with the frequency ofthe control circuit and low in comparison with the natural frequency of the crystal element, this improved relay device can function as a converter to provide the secondary or controlled circuit with biased toward the crystal-carried contact point 76 unidirectional current pulses which may be utilized in any desired manner.

Should greater sensitivity be required than is obtainable by the device thus far described, as well as lessened time lag, the resilient secondary contact may be omitted and the secondary, or controlled circuit, b changed to the closed" type. In that case, exemplified by the dotted connection 31 in Figure 1, the contact point I! carried by the crystal element and the contact point 11 carried by the oscillatory device ar included serially in the secondary circuit. These points, when the relay is not energized, are in" engagement.

To actuate the relay, either unidirectional potcntial oi the proper polarity, or alternating potential, may be applied momentarily to the crystal element electrodes. If the potential is unidirectional, a single sharp impulse is given to the oscillatory device inthe direction of the arrow B, and the said device, because of its inertia, cannot follow the crystal back to the rest position, but continues its rotary movement thus breaking the secondary circuit and actuating the controlled mechanism. After a definite time interval, the oscillatory device rotates back to the rest position in the direction of the arrow A, the secondary circuit is again closed and, provided that the primary circuit has been opened in the meantime, the relay may again be actuated by closing the primary circuit.

A bleeder resistor 39, having a resistance of from 1 to 10 megohms, is connected across the crystal electrodes to drain the charge acquired thereby at each actuation of the relay.

In the event that the primary or control potential is alternating, the crystal element may or may not be made resonant thereto. The action in response to alternating potential, at high frequency, is a periodical interruption of the secondary circuit, at some rate determined by the inertia of the oscillatory device and th magnitude of the primary potential. terruption is lower than the frequency of the control potential, yet, if desired it may be made sufficiently high, by properly choosing the frequency and magnitude of the control-potential, so that the net eiTect is a reduction of the secondary current rather than complete interruption thereof. An inductor 4i may be included in the secondary circuit for smoothing purposes.

In the event that it is desired to provide a relay, according to this invention, that shall be extremely sensitive to the frequency of the control-circuit, it is preferred to make use of the low amplitude longitudinal vibration of a crystal rod or the like. 1

Referring now to Figure 2 of the drawing, such modification of this invention may comprise a crystal section 42 of the type adapted to expand and contract longitudinally upon the application of alternating potentials to a plurality of electrodes 43 and 45 properly associated therewith as is already known to those skilled in the art. The crystal bar, which may be of quartz or the like is so cut and supported at one end 41 that its natural resonance frequency coincides with the frequency of the control potential.

The free end 49 of the crystal carries a contact point 5| that is comprised in an electrical circuit which may include a resistor 53, a source of potential 55, the primary winding 51 of a transformer and a conductive cam shape device 59 pivotally mounted for rotary movement about a horizontal axis. The riser 6| of the cam shape device projects over the contact point 5| mounted upon the free end of the crystal and it may carry a second contact point 63. The cam shape device is so proportioned that the free end of the riser carrying the contact point 63 is normally biased into engagement with the contact point 5 I' carried by the crystal element and unidirectional current,

The rate of inlimited by the resistor in the circuit, flows in th is shown, it is to be understood, of course, that it Ill) may be given any other contour provided that it is overbalanced or biased in the direction of the arrow C and that it has an appreciable moment of inertia around the pivotal point 65.

Furthermore, a spring suspended mass may be.

utilized in lieu of th pivoted device without departing from the scope of this invention, or if the control frequency is relatively low, a Rochelle salt element may be substituted for the quartz bar.

When alternating potentials ar applied between the crystal-electrodes, the crystal element expands and contracts in synchronism therewith and, at frequencies removed from th resonance frequency thereof, such elongation and contraction is comparatively small. At resonance, however, taking for example a bar of Rochelle salt having a natural frequency of 30,000 cycles, the movement of the contact point carried by the end of the crystal may be of the order of two tenthousandths of an inch. Considering one-half cycle of the applied potential, the contact point carried by the crystal element moves upward and back to the mean position in one sixty-thousandth of a second and it gives the contact point carried by the cam shape device a sharp impulse upward. Because of the inertia of the cam and the elasticity of the contact points, the first im pulses have minor effect but as excitation of the crystal at its resonant frequency continues the cam finally acquires sufficient angular momentum so that the secondary circuit is broken at the contact points. After a time interval, however, determined by the are through which the. device moves after contact is broken, it will tend to return to the rest position but it will be met by the rapidly vibrating contact point on the end of the crystal element from which it will receive another series of unidirectional impulses. Each time the cam shape device receives a series of mechanical impulses from the crystal, the secondary circuit is momentarily mad and immediately thereafter broken, thus causing a train of unidirectional current pulses to flow in the primary winding of the transformer, the time-spacing of the pulses being determined by the throw of the cam shape element. In the above described modification of this invention, a conversiondevice is provided whereby alternating current may be caused to flow in a secondary circuit upon the receipt of very minute alternating control currents, at a very much higher frequency. The relay is extremely selective with respect to the primary frequency, and it is also substantially unaffected by climatic or other changes which cause the contact points of usual piezoelectric relays to vary in spacing.

Both embodiments of this invention may, of course, comprise sections or bars cut from crystals of quartz, tourmaline, Rochelle salt, orany' other material that exhibits piezoelectric properties. Furthermore, it is within the scope of this invention to substitute a steel rod or bar for the crystal element disclosed in Figure 2 and to excite the bar at its natural frequency by one or more crystal elements or to excite it magnetically should it be made from magnetostrictive material. These last mentioned modifications are believed so obvious as to require no additional-illustration.

In accordance with this invention, a buzzer," so tospeak, may also be provided, whereby a unidirectional control potential may be utilized directly for the production 01* alternating current, or the buzzer may be actuated from a unidirectional source to periodically interrupt a secondary circuit to supply current or potential pulses.

Referring now to Figure 3 of the drawing, it will be noted that the electrodes 9 and II afllxed to the crystal element I are comprised in a circuit that includes the contact point I! carried by the pivoted oscillatable device, a source of potential 81, a switch 33 and the slip-ring 29. A secondary or controlled circuit 23 may be connected to the pivoted contact member in essentially the same manner as is exemplified by Figure 1.

If desired, the control circuit may be broken at X" and the primary winding of a transformer H be included therein.

The operation of the modification illustrated in Figure 3 is as follows:

Assume that the pivoted device is resting upon the contact point carried by the crystal element and is biased against it by gravity. If the switch 33 is now closed and the polarity of the applied potential from the source is correct, the free end of the crystal element will be sharply deflected upward and the pivoted device 'will be given a unidirectional impulse in the direction of the arrow B. Because of its inertia the pivoted device continues rotating to break the primary circuit and, if the arc of travel thereof is sufilcient, to thereafter close the secondary circuit which thereupon supplies a pulse of current to the controlled device 23 which may be a relay, a transformer followed by a rectifier, or the like. The breaking of the primary circuit removes potential from the crystal element and the charge leaks oil through the resistor 39 connected in shunt to the crystal-electrodes, The crystal section, being deprived of potential, returns to its normal unstressed position before the pivoted contact member completes its return rotation in the direction of the arrow A, at which time the above described sequence of operations is once more initiated. The pivotedmember, therefore, may be maintained in a state of oscillation, the period of which is determined by the arc of movement away from the rest" position.

Not only will the device function as a buzzer upon the application of direct current thereto as described, but it will also act in the same manner if alternating potential is applied to the crystal electrodes.

The current pulses in the primary circuit may be converted into alternating current by the transformer H, and thereafter utilized in any that a pendulum, or the like, may be utilized in lieu thereof.

One of the most important features of this invention is the provision of an oscillatable device, or the like, exemplified in the drawing by the pivoted elements l and 53, the inertia of which is so high as to prevent them from following back the contact point carried by the crystal element accuse immediately after it has once received a unidirectional impulse therefrom. Having such characteristics, when the relay is energized, the pivoted or otherwise supported mass engage; the contact point carried by the crystal element periodically at a frequency substantially uninfluenced by any variation in the frequency of the control potential, and thus -a definite time-delay may be introduced into the relay operation.

Should it be desired that there be no appreciable delay between the application of the controlpotential to the crystal element and the closing of a secondary circuit, the resilient contact element [3 may be replaced by a small wiping contact 13 disposed in the path of movement of the pivoted member. If a wiping contact is utilized, the secondary circuit is closed almost immediately upon the closing of the primary control clrcuit by the switch 33 and it remains closed until the pivoted member has returned to its rest" position. Instead of a wiping contact a switch of the togg1e" type actuated by a projection (not shown) on the pivoted member may be utilized, and it further lies within the scope of this invention to provide the said pivoted member with a plurality of conductive projections (not shown), each of which, when engaging the wiping contact 13, causes an impulse in the secondary circuit.

There is a tendency for the pivoted member to chatter when it returns to the normal position. One way of preventing chattering would be to mount a small friction pad 15 adjacent the rest position of the pivoted member, as shown in Figure 3, which pad rubs slightly against the surface of the said member.

This invention is also applicable to reversible relays i. e., relays oi the on-oil" type or of the type wherein control current of one polarity closes one set of secondary contacts and opens another set while control current of the opposite polarity opens the previously closed set of contacts and closes those already open.

A relay of such general type is exemplified by Figure 4 of the drawing and it may comprise a piezo-electric element of the same type as shown in Figures 1 and 3. For the purpose of rendering the relay reversible in action, a balanced element having appreciable inertia, such as a disc 11 mounted upon a pivot 19 to rotate in a vertical plane, is disposed adjacent to the free end 5 of the crystal element in mechanical energytransfer relation thereto. To permit such energy transfer, the periphery of the disk may be provided with a notch 8| into which the free end 5 of the crystal element projects. A similar notch 83 may be provided in another portion of the periphery of the disc into which extends a plurality of electrical switches 85 and 81, each switch being constituted by at least two spring elements carrying contact points, the said points normally being biased to the open position.

For the purpose of holding the disc in one of two positions, it may be provided with an axially projecting pin 89 that engages a spring 9|, the said pin and spring offering only slight resistance to rotation of the disc but the force of engagement being sufficient to hold the disc when it is displaced to either side beyond the balanced position.

The relation of the several switch assemblies with respect to the notch in the disc is such that whenever the said disc is displaced a slight angular distance beyond the balanced point, one of the switches is closed and the other one is permitted to open. The relation of the other notch in the disc to the free end of the crystal element is such that the disc, when at rest, is in contact with the upper or the lower face of the crystal element, or with contact points carried thereby, also depending upon the angular position of the disc with respect to the balanced position. The several positions of the disc are exemplified by the dotted lines.

To understand the operation of this embodiment of the invention, assume first that the relative position of the disc crystal element and switches is as shown in the drawing, the point carried by the lower face of the crystal element being in contact with the inner surface of the adjacent notch, the upper switch 85 being closed, the lower switch 81 being open and the pin 89 being to the right of the central or balanced position and being lightly retained in such displaced position by the spring N. If, now, potential of proper polarity is momentarily applied-to the crystal element to cause it to suddenly bend downward, a sharp impulse will be transmitted to the balanced disc and it will be given an impetus in the direction of the arrow D. Because of the inertia of the disc, it will tend to continue its rotation, the spring will permit the pin to pass through the dead center position and the upper switch 85 will be permitted to open while the lower switch 81 is caused to close because of the engagement therewith of the lower corner of the notch 83 into which the switches project. The placing of the spring 9! with respect to the pin is such that the disc will be prevented from returning to the initial position and the lower set of switch contacts will be held closed until potential of opposite polarity is applied to the c ystal element.

Should the crystal tend to "set either upwardly or downwardly a slight amount, this only results in one or the other set of switch contact points being held more firmly in engagement after contact has once been made.

Instead of using unidirectional potentials for actuating the switch, alternating potentials may be utilized provided the frequency is high with respect to the duration of the control impulse.

That is to say, the disc will respond to rapid vibration of the free end of the crystal element in substantially the same way as the device exemplified by Figure 2 responds, provided that the amplitude of movement of the free end of the crystal occasioned thereby is not greater than the angular widthof the notch 81 associated therewith and provided further that the duration of the controlling impulse is short as compared with the time required for the disc to be set into rotation.

It is not to be inferred from the foregoing that the invention is limited to a disc rotating in a vertical plane inasmuch as the same result is wined when the axis of the disc is vertical. It should also be clear that the disc and the contact points mounted upon the free end of the crystal element may also be included in a controlled or secondary circuit. Furthermore, the notches may be replaced by suitable pairs of axially projecting pins and many other structural modifications are possible without departing from the spirit of this invention.

It will be apparent from a consideration of the foregoing description of several'specifl'c embodiments of this invention that a novel piezoelectric relay or conversion device, is provided, that is not adversely affected by set or sag of the piezoelectric element. In addition, the improved relay is not dependent upon the type of potential utilized for control, it being equally as well responsive to unidirectional as to alternating potentials. Another advantage of the invention resides in the automatic time lag obtainable in the operation thereof, which lag is built in the device and is not secured electrically as is the case with systems of the type exemplified by the Mason Patent 2,166,763 and the Blattner et al. Patent 2,201,879. In this connection, it should be noted that the capacitor connected in shunt to th control switch and, the capacitor connected in shunt to the secondary contacts have no hearing upon the operation of the relay per se when considered from the time lag standpoint; these capacitors serve their usual and customary purpose of preventing excessive sparking.

Many other modifications and adaptations of, as well as additions to this invention will be apparent at once to those skilled in the art to which it pertains. This invention, therefore, is

not to be limited except insofar as is necessitated by the prior art and by the spirit of the appended claims.

What is claimed is:

1. In combination, a piezoelectric element mounted for vibratory movement upon the application of suitable potential thereto, and an independent oscillatable device disposed in such energy-transfer relation therewith as to receive only unidirectional mechanical impulses therefrom, the said .device having high inertia.

2. The invention set forth in claim 1, characterized in that the mass of the oscillatable device is sufiiciently high and the restoring force acting thereon sufflciently low that it is inherently precluded from following the return movement of the piezoelectric element immediatel after receiving an impulse therefrom.

3. The invention set forth in claim 1, characterized in that the oscillatory device is normally biased into energy-transfer relation with the piezoelectric element.

4. The invention set forth in claim 1, additionally characterized in that the piezoelectric element is of the type wherein set or sag occurs during utilization thereof in a relay or the like.

5. The invention set forth in claim 1, additionally characterized in that the piezoelectric element is a mixed tartrate of the Rochelle salt type.

6. In a relay, an element adapted to develop mechanical force upon the application of electrical potential thereto, an independent oscillatable ,device having high inertia mounted in energy-transfer relation therewith to receive short unidirectional mechanical impulses therefrom, and means whereby the electrical condition of a secondary circuit may be rendered responsive to the position of the oscillatory device.

'1. In a conversion device, a piezoelectric element at least one portion of which is adapted to move in response to an electrical potential applied thereto, an electrical contact point actuated by said portion, an independent mechanica1 oscillatory device mounted in energy-transfer relation with the piezoelectric element to receive unidirectional impulses therefrom, the inertia of the device being high, a contact point movable by the oscillatory device into and out of engagement with the first mentioned contact point and 'points to the closed position, whereby the relay operates as a buzzer" so long as a potential is applied to the piezoelectric element over a circuit including said points.

9. The invention set forth in claim 7, wherein the restoring force applied to the oscillatory device is in such direction as to bias it toward energy-transfer relation with the piezoelectric element.

10. The invention set forth in claim 7, further characterized in'that means are provided whereby the electrical condition of a secondary circuit may be rendered responsive to the position of the oscillatory device.

11. A relay comprising a piezoelectric element, a primary control circuit connected thereto, means energizable from said element for opening and closing a secondary circuit, and mechanical means for timing the operation of the relay.

12. As an article of manufacture, a relay comprising a piezoelectric element responsive to a control-potential, means energized therefrom for determining the condition of a secondary circuit, and inertia controlled means for timing the operation of the relay.

13. In a relay, a piezoelectric element having a free portion adapted to move when potential is applied to the element, an independent electrical switch so mounted adjacent to the crystal element as to be capable of receiving unidirectional actuating impulses therefrom, the switch being of such type that,upon-action thereof having been once initiated, it carries through automatically to completion.

14. In a relay, a piezoelectric element, an electrical switch mounted adjacent thereto to be actuated thereby, and means whereby "set or sag of the crystal element during utilization thereof is precluded from interfering with normal relay 7 operation.

15. In a relay, a piezoelectric element adapted to move upon the application of electrical potential thereto, an electrical witch, and means for transferring motion therebetween, said means including an instrumentality for minimizing the effect of crystal element sag upon operation of the relay.

16. In a relay, a piezoelectric element adapted to move upon the application of electrical potential thereto, an electrical switch comprising a first contact that partakes of the motion of the crystal element, a second contact, and osclllatable inertia means tending in the quiescent state to bias the second contact into engagement with the first contact, the natural frequency of the piezoelectric element being high in comparisonto the period of the oscillatable means.

17. In a relay, a piezoelectric element adapted to move suddenly in response to the application of electrical potential thereto, and also subject to slow movement or set in response to-natural causes, and a control device having a part in'operative relation to said element to be actuated thereby, the combination being characterized by the utilization of inertia for ensuring operation of the relay despite the tendency of said element to move slowly in response to natural cause other than the intentional application of electrical potential.

18. The invention as set forth in claim 1, characterized in that the oscillatory device is normally gravity-biased into energy-transfer relationship with the piezoelectric element.

19. The invention as set forth in claim 1, characterized in that said oscillatory device is normally spring-biased into energy-transfer relationship with the piezoelectric element.

20. In a relay device for repeated actuation of control means; a piezoelectric element, means for repeatedly applying an electrical charge to said piezo electric element to cause said piezoelectric element to actuate said control means, and resistor means connected to said piezoelectric element to dissipate at least part of one charge on the said piezoelectric element before the next charge is applied thereto.

21. The invention as set forth in claim 20 further characterized by the charge applied to said piezoelectric unit being an alternating charge.

22. In a relay, a piezoelectric element having a first portion adapted to move with respect to a second portion upon application of electrical potential thereto, mounting means engaging the second portion of said piezoelectric element for at least partially supporting said element, an electrical switch, and inertia means having appreciable inertia movably mounted with a portion thereof in energy transfer relationship with said first portion of said piezoelectric element for actuating said electrical switch upon rapid movement of said piezoelectric element, said means for mounting said inertia means permitting slow limited movement of at least said first portion of said piezoelectric element without actuation of said switch.

ALFRED L. W. WILLIAMS. 

